Submitted to: Enzyme and Microbial Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/18/2008
Publication Date: 4/1/2008
Citation: Nichols, N.N., Sharma, L.N., Mowery, R.A., Chambliss, C.K., Van Walsum, G.P., Dien, B.S., Iten, L.B. 2008. Fungal metabolism of fermentation inhibitors present in corn stover dilute acid hydrolysate. Enzyme and Microbial Technology. 42(7):624-630. Interpretive Summary: Use of crop residues to make value-added products is complicated by side-products that form when biomass is pretreated to obtain usable sugars. The mixture of side-products is toxic to microbes and can prevent successful fermentation of the sugars. We previously isolated a soil fungus that can metabolize a large number of those inhibitory compounds. In the present study, we followed the fate of the side-products in pretreated biomass and determined that the fungus removes all of the major and many of the minor inhibitory compounds from the mixture. Treatment of the biomass sugars in this way improved the performance of ethanol fermentations. Conditioning of pretreated biomass, to remove inhibitory compounds, is often complex and expensive with existing technology. The biological abatement approach described here could provide an improved method for removing inhibitors from biomass-derived sugars.
Technical Abstract: Use of agricultural residues for ethanol production requires pretreatment of the material to facilitate release of sugars. Physical-chemical pretreatment of lignocellulosic biomass can, however, give rise to side-products that may be toxic to fermenting microorganisms and hinder utilization of sugars obtained from biomass. Potentially problematic compounds include furans formed by degradation of sugars, organic acids released from hemicellulose side-groups, and aldehydes and phenolics released from lignin. A fungal isolate, Coniochaeta ligniaria NRRL30616, metabolizes furfural and 5-hydroxymethylfurfural (HMF) as well as aromatic and aliphatic acids and aldehydes. NRRL30616 grew in corn stover dilute-acid hydrolysate and converted furfural to both furfuryl alcohol and furoic acid. Hydrolysate was inoculated with NRRL30616, and the fate of pretreatment sideproducts was followed in a time-course study. A number of aromatic and aliphatic acids, aldehydes, and phenolic compounds were quantitated by analytical extraction of corn stover hydrolysate, followed by HPLC-UV-MS/MS analysis. Compounds representing all of the classes of inhibitory side-products were removed during the course of fungal growth. Biological abatement of hydrolysates using C. ligniaria improved xylose utilization in subsequent ethanol fermentations.